Collapsible crab pot is a common fishing gear that has been operated by many fishermen, however this kind of fishing gear has a low selectivity. The selectivity level of crab pot needs to be increased so that the size of crab catch comply to the allowable legal size. Fishing trials of crab pot with the mesh size of 1¼, 2, 2½ and 3 inch square-shaped has been done in the waters of north Lamongan, East Java. The objectives of this research is to determine the effect of mesh size to the number and size of the catches. The results showed that different mesh size has significant effect on the catch of pot. However the catch of a 2 inch mesh size pot (of 2.17 kg / setting) was not significantly different with the catch of pot with 1¼ inch mesh size (of 2.08 kg / setting). Percentage of BSC catch with carapace width (CW) > 100 mm increased by increasing of mesh size of net. The highest percentage (98 % of the total catch) was obtained from the 3-inch mesh sizes.